We have demonstrated that immobilized IgG aggregate or IgG-erythrocyte complexes, lacking target cell specificity, may induce lysis of erythrocytes by normal human peripheral blood lymphocytes (PBL). The reaction induced by immobilized IgG aggregate can be distinguished from that induced by IgG-erythrocyte complexes by differences in susceptible target cells, kinetics and suppression by other cells. Furthermore, both reactions are easily distinguished from antibody dependent cell-mediated cytotoxicity (ADCC) and natural or spontaneous cell-mediated cytotoxicity (NCMC). During the next budget period we will attempt to further define these reactions. Comparisons will be made between ADCC, NCMC, immobilized aggregate and IgG complex induced cytolysis. Special emphasis will be placed on the difference in target cells lysed in IgG aggregate and IgG-erythrocyte complex induced cytolysis (IgG erythrocyte induced lysis is specific for SRBC). Effector cells and suppressor cell characteristics will also be determined.